The cranium of a human infant is made up of frontal, parietal, temporal, occipital and other smaller bones that are separated by membranous intervals until brain growth is complete at eighteen to twenty-four months of age. Normally, the infant cranium is symmetrical in shape. However, in the condition known as plagiocephaly, the head is non-symmetrical, becoming parallelogram or rhomboid shaped. Sometimes the plagiocephalic head may correct its shape over time, but often the condition may persist, leading to facial asymmetry with functional, cosmetic, and other disabilities. If orthotic treatment is indicated, it is important to attempt correction of the deformation when the subject is less than a year old, before the sutures in the cranium have solidified.
The shape of the infant cranium is determined by multiple factors including brain growth and development, constraints placed on the skull during and after gestation and bony abnormalities of the skull. When an infant's head is maintained in a nearly fixed position either in utero or when sleeping on a flat surface, the cranium may be progressively deformed. A condition known as occipital positional plagiocephaly or deformational plagiocephaly frequently occurs in children who sleep in a relatively constant position on their backs. For example, as a result of the American College of Pediatrics recommendation that children be placed on their back instead of on their stomach to avoid SIDS (Sudden Infant Death Syndrome), a significant number of new cranial deformities are being seen (Argenta, L. C., et al., J. Craniofac. Surg. 7:5–11 (1996)). In addition, many infants have craniums that are deformed either in utero or during the birth process, and sleeping on the depressed portion of the skull accentuates the deformity. Infants who are slower to develop motor activity may also develop cranial abnormalities because of their failure to move their heads frequently. Finally, in some cases plagiocephaly is secondary to synostosis, a condition in which some of the skull sutures fuse too soon, making the skull bulge somewhere else.
Unfortunately, surgery is often the treatment prescribed to correct plagiocephaly of the infant skull. While plagiocephaly secondary to synostosis usually requires surgery, many deformities of the skull can be corrected with appropriate molding helmets (Argenta, L. C., et al., J. Craniofac. Surg. 7:5–11 (1996); Claren, S. K., et al., J. Pediatrics 94:43–46 (1979)). Such helmets take advantage of the pliability of the infant skull to mold the skull into a normal shape.
There are basically two types of corrective infant helmets. An active helmet is a device that places an active constricting force on the skull to force it to grow in a more normal fashion. These helmets are marketed as Dynamic Orthoplast Cranioplasty (DOC) helmets. In general, active DOC helmets must be custom fitted, require greater amounts of time for fabrication, and must be changed frequently as the infant head increases in size. As a result, DOC helmet therapy requires multiple clinic visits and may cost in the range of several thousands of dollars per patient. In addition, placing a constricting force on the growing brain is not thought to be physiological by most physicians.
Passive helmets or soft shell helmets attempt to take pressure off of the deformed portion of the skull, thus allowing the brain to grow in a more normal fashion. Thus, in contrast to active molding, passive helmets provide for a more gradual and physiological correction of skull shape.
A graded series of sized helmets for treatment of infant plagiocephaly were described in U.S. Pat. No. 4,776,324 to Claren. The Claren helmet is generated based on horizontal and transverse imaging measurements of either a patient skull or the skull of a normal infant. The Claren helmet fully encloses the head, and is designed such that it is slightly larger than the patient's skull. The helmet uses passive molding in that the head grows into the helmet. A graded series of prefabricated helmets are required as an alternative to the previous technology using individualized helmets shaped to each patient's skull.
Although full helmets are effective in treating plagiocephaly (Argenta, L. C., et al., J. Craniofac. Surg. 7:5–11 (1996)), they are confining and uncomfortable. Additionally, the use of several helmets is cumbersome and it can be difficult to match the individual patient's skull with the prefabricated helmets available. Alternatively, the helmets which are generated based upon the patient's individualized skull shape are expensive and time consuming to produce.
A cranial remodeling band using active molding to treat plagiocephaly is described in U.S. Pat. No. 5,094,229 to Pomatto. Pomatto described a cranial remodeling band with an internal surface which reflects the desired reconfiguration of the subject's cranium. The technology employs active molding, in that it applies corrective forces to those regions of the cranium which protrude. The technology is expensive, however, in that effective therapy requires that the orthosis be individualized for each subject, and a series of helmets is required for each infant.
A helmet to correct brachycephalic cranial abnormalities is described in U.S. Pat. No. 5,308,312 to Pomatto. The brachycephalic head is expressed as an occipital flattening of the cranium such that the maximal cranial breadth is disproportionately large in relation to the maximum cranial length. The helmet described in U.S. Pat. No. 5,308,312 is designed to address a unique form of abnormal head shape. However, the helmet has many of the disadvantages of other helmets, e.g., for maximum effectiveness, the helmet must be fabricated from an impression of the individual subject's head.
Thus, there is a need to develop corrective infant helmets that provide a gentle but effective therapy for the large majority of plagiocephalic infants. Rather than squeezing unaffected regions of the infant brain, it would be preferable to relieve the pressure from depressed areas of the skull. To enable correction of the abnormality before the brain plates begin to fuse, a helmet must be comfortable enough to be worn for the extended periods of time, up to 23 hours a day. In addition, such therapeutic helmets should be affordable and accessible to the many patients who require treatment.